For friction materials, such as brake pads, brake linings, and clutch facings for various vehicles and industrial machines, mixtures obtained by dry-mixing a binder such as a thermosetting resin, an inorganic filler such as a titanate compound, an organic filler, and so on are conventionally used. Such a mixture is formed into a shape at a predetermined pressure and normal temperature, then thermoformed at a predetermined temperature, and then subjected to thermal treatment and finishing, resulting in a formed body of a friction material or so on.
As the titanate compound, alkali metal titanates represented by a general formula M2O.nTiO2 (where M is an alkali metal element) are used. Because, however, alkali metal titanates in which n=2 to 4 have a lamellar crystal structure, their interlamellar alkali component may be eluted during formation of a friction material, thus deteriorating the matrix resin of the friction material. On the other hand, alkali metal titanates in which n≧6 cause less elution of an alkali component but have insufficient wear resistance.
Patent Literature 1 discloses that the elution of an alkali component contributes to the formation of a friction film and a transfer film at the frictional interface. In view of this, Patent Literature 1 proposes to use an amorphous alkali metal titanate and a crystalline alkali metal titanate of n≧6 in combination and allow a suitable amount of alkali component to be eluted by wear failure, softening, melting, and so on of the alkali metal titanates due to friction, thus improving the wear resistance. Patent Literature 2 proposes to coat the surface of an inorganic filler with phenolic resin to improve the wear resistance.